(a) Field of the Invention
The present invention relates to a control method for a powertrain system of a hybrid vehicle. More particularly, the present invention relates to a control method for a powertrain of a hybrid vehicle in a compound split mode.
(b) Description of the Related Art
Hybrid vehicles have become increasingly popular over the last couple of years due to their high fuel efficiency and low impact on the environment. A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors powered by a battery. However, alternative forms of hybrid vehicles do exist, Hybrid Fuel cell vehicles.
A hybrid vehicle may operate in various control modes based on the vehicle's driving conditions. For example, a hybrid vehicle operate in FG (fixed gear) modes and EVT (electrical variable transmission) modes of which speed and torque are controlled using a plurality of planetary gear sets, an engine, and a motor/generator.
While operating in EVT modes, in a compound split mode (e.g., EVT2), a first motor/generator MG1 is used for controlling a driving point of an engine (i.e., speed control of the engine), and a second motor/generator MG2 is used for controlling engine torque and compensating for demand torque.
During the compound split mode (EVT2 mode), when the driving point of the engine increases, the MG1 executes speed control to follow the engine driving point. However, efficiency of following the engine driving point and demand torque output may vary based on a control method of the MG2.
Conventionally, the control method of MG2 is used for compensating for engine torque. When the current speed of the engine does not follow a target driving point, the MG1 outputs a maximum output for following the target driving point. Simultaneously, the MG2 maintains a maximum output for satisfying demand torque when the engine speed does not increase sufficiently. In this case, since compensating torque of the MG2 increases, the efficiency of following the engine driving point and SOC (state of charge) balancing may be further deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.